Optimizing Bidirectional AC Charging Efficiency of Multilevel Batteries: A Simulation Approach

This paper investigates the optimization of bidirectional Alternating Current (AC) charging efficiency for modular Multilevel Inverter (MLI) based reconfigurable battery systems in the context of electromobility. This shall be achieved by the selection of a suitable Sub module (SM) topology within the MLI battery system. A simulation environment is developed to analyze the current Total Harmonic Distortion (THD), inverter efficiency, and battery efficiency of different MLI SM topologies. Specifically, comparisons are made between half bridge and Battery Modular Multilevel Management (BM3) SM topologies under various charging current and phase angle scenarios within the boundaries of the Type 2 Mode 3 charging standard of the European power grid. A boxed inverter design combined with a Cascaded H-Bridge (CHB) meso topology was used and peripheral influences through line resistance and line inductance were considered. Results indicate low THD values for both systems, with similar efficiencies close to theoretical maxima, albeit with slight advantages favoring the BM3 topology at higher currents. Battery efficiency remains consistently high, with marginal benefits favoring the BM3 system. Future research will explore the cost-effectiveness of employing multilevel systems for bidirectional AC charging, considering potential advantages over conventional AC onboard chargers.